Group 13-16 materials, and in particular, gallium arsenide (GaAs), have been employed recently in an increasing variety of electronic and electro-optical uses. For example, integrated circuits which are based on active layers of gallium arsenide, such as metal insulator semiconductor field-effect transistors (MISFETs), monolithic microwave integrated circuits (MMICs), and fast-logic circuits, have been employed in digital signal processing for military, biomedical, and communicationsystems applications. Gallium arsenide has also been employed in the fabrication of minority charge-carrier devices, such as solar cells and photodetectors. In addition, optical sources, such as lasers and light-emitting diodes (LEDs), have been developed which are of Group 13-16 materials, such as GaAs for the lasant medium.
However, surface states of gallium arsenide provide sites for non-radiative recombination. Therefore, passivation is generally required to maintain the mobility of charge carriers. Examples of known methods of passivating gallium arsenide include deposition or growth of oxides, nitrides or sulfides by various techniques, such as molecular beam epitaxy (MBE), physical vapor deposition (PVD), or electrochemical deposition.
Alternatively, buffer layers are enclosed to provide an intermediate transitional layer between a semiconductor substrate and subsequent layers to be formed over the substrate. For example, high-resistance buffer layers isolate circuits formed in active gallium arsenide layers from the underlying substrate. See, for example, U.S. Pat. No. 4,952,527, issued Aug. 28, 1990.
There are several problems associated with known methods of passivating gallium arsenide and with forming buffer layers on gallium arsenide For example, more than one chemical precursor is typically required to form the chemical compound deposited on gallium arsenide substrate. Use of multiple precursors often causes formation of impurities and consequent irregular composition of the passivating/buffer layer by incorporation of impurities in the passivation layer during deposition. Further, some passivating/buffer layers, such as arsenic trisulfide, which can be formed by known methods, are often toxic. In addition, sulfurizing techniques generally form passivating layers which are relatively unstable. Also, known methods for deposition of passivating/buffer layers often require exposure of the gallium arsenide substrate to high temperatures, which can degrade the substrate. In addition, there are other problems commonly associated with known methods of deposition, such as slow deposition rates, and the requirement of expensive, complicated equipment for conducting deposition on gallium arsenide substrates.
Therefore, a need exists for an improved method for forming a passivating/buffer films on gallium arsenide or other semiconductor substrates, which overcome or minimize the above-listed problems.